1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic printer, a copying machine, or the like.
2. Description of the Related Art
There are known some image forming apparatuses, such as a printer and a copying machine which have a measurement device for measuring the amount of toner deposited on an image carrier, so as to correctly compensate, for image density change under the influence of environmental changes, secular changes, and the like. Such a measurement device has a light source for emitting a light beam to an image carrier, and which receives the reflected beam from the image carrier to measure an amount of toner deposited on the image carrier. In such a measurement device, toner particles scattered from the image carrier may be attached to optical members of the device, such as a cover glass or a lens adjacent to the image carrier. Accurate measurements cannot be performed when the toner particles are attached to the optical members.
Not only in the measuring device for measuring the amount of toner, but also in devices, such as a laser optical system, a solid-state scanning head, and the like, which have a light-emitting unit and a light-receiving unit, scattered toner particles may be attached to optical members, such as an exposure mirror, a cover glass, or a lens, which are arranged in the optical path of the device, and a change in exposure amount or the scattering of emitted light occurs. In this case, the device cannot operate correctly, and it is difficult to form accurate images.